Phase portrait of two candidate fixed structure control strategies for the oscillator system with <i>ξ</i> = 0.7.

<p>Left: (a) Stable dynamic (poles at −0.35 ± 0.69<i>j</i>). Right: (b) Unstable dynamic (poles at 0.5 and −1.2). In (a), the trajectories move in a clockwise motion to reach the origin. In (b), the trajectories move away from the origin except along the asymptotes of the hyperbolic structure in the quadrants with .